This application claims priority of Korean Patent Application No. 10-2003-0068367 filed on Oct. 1, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates generally to an apparatus for conveying substrates, and more particularly to an apparatus which supports a substrate on a substrate supporting unit and conveys the substrate supporting unit by use of rollers.
2. Description of the Related Art
Substrates have been applied to various products, for example, Flat Panel Displays (FPDs) such as Liquid Crystal Displays (LCDs) and Plasma Display Panels (PDPs). Because these products are manufactured through a plurality of processes, each of the substrates must be conveyed to desired processing units for required processes. In order to convey the substrate to the processing units, there have been proposed a variety of substrate conveying apparatuses.
Generally, in a substrate processing system, a plurality of processing units which perform a coating process, a developing process, and an etching process, respectively, are installed at predetermined positions of a substrate conveying apparatus. Of the conventional substrate conveying apparatuses, there has been used an unmanned conveying vehicle called an automatic guided vehicle (AGV). The AGV loaded with a substrate cassette which contains about twenty substrates travels between the processing units. Because a conventional LCD glass substrate is small, ranging from 300 mm2 to 500 mm2, several sheets of LCD glass substrates may be contained in one substrate cassette and conveyed to the plurality of processing units using the AGV.
However, there is a growing tendency that the LCD glass substrates have increased in size. Recently, the LCD glass substrates having surface areas of 1 m2 or larger have been used. When the large LCD glass substrate is contained in the cassette, the substrate may be undesirably bent. Therefore, the conventional AGV has been restricted in conveying the cassette containing the large and heavy substrate.
The conventional AGV has another problem since the AGV is very expensive, for which the number of the AGVs provided on one substrate processing system is restricted, thus deteriorating an operational efficiency while processing the substrates.
Further, among the conventional substrate conveying apparatuses, there are a roller conveyor and an air cushion conveyor. The roller conveyor conveys the substrates one at a time. The air cushion conveyor conveys the substrates using pneumatic force and rollers. However, the conventional roller conveyor and the conventional air cushion conveyor have problems in that the substrates continuously contact the rollers while the substrates are being conveyed, thus impurities may contaminate contact parts of the substrates on which the substrates contact the rollers, and a contact stress may occur on the contact parts of the substrates.
Further, when each of the substrates is conveyed to the processing units to go through a required process, by the conveying apparatus, the conveyance of the substrate may be delayed because there is a difference in the processing time according to a kind of process which is performed on the substrate or a kind of substrate. To buffer the difference in the processing time, another type of substrate processing system which collaterally has a buffer function to temporarily store the substrate has been proposed. In order to add such a buffer function to the substrate processing system, various methods have been used. Among these methods, there is a method of temporarily stopping the substrate conveying apparatus. However, the method of stopping the substrate conveying apparatus to provide the buffer function has a problem in that a throughput is undesirably reduced.